1. Field of the Invention
The present invention relates to semiconductor design and manufacturing. More specifically, the present invention relates to a method and apparatus for determining whether a sub-resolution assist feature will print.
2. Related Art
Dramatic improvements in semiconductor manufacturing technologies presently make it possible to integrate tens of millions of devices onto a single chip.
Semiconductor manufacturing technologies typically include a number of processes which involve complex physical and chemical interactions. Since it is almost impossible to find exact formulae to predict the behavior of these complex interactions, researchers typically use process models which are fit to empirical data to predict the behavior of these processes. A process model can be used in a number of applications during the design of a semiconductor chip. For example, process models are commonly used for making corrections to layouts to compensate for undesirable effects of semiconductor manufacturing processes.
One of the important steps in semiconductor manufacturing involves placing assist features in a layout. Assist features (AFs) can be printing (e.g., super-resolution assist features) or non-printing (e.g., sub-resolution assist features). In either case, assist features are meant to improve the depth of focus of the layout.
The larger the SRAF (sub-resolution assist feature), the more effective the SRAF will be in improving a pattern's manufacturing robustness. However, larger SRAFs are also more likely to print on a wafer. Hence, to determine the optimal SRAF width, we need to accurately predict when an SRAF will print.
Unfortunately, process models created using prior art techniques usually cannot accurately predict when an SRAF will print. As a result, foundries typically use very conservative SRAF widths (i.e., overly thin SRAFs) everywhere on the wafer, thereby forfeiting the advantages of using SRAFs.
Hence, what is needed is a method and an apparatus for accurately determining whether a sub-resolution assist feature will print.